The nozzle end of one type of electromechanical actuated fuel injector comprises a frustoconical valve seat that funnels to a central circular hole that is covered by a thin disc orifice member having one or more orifices. An internal actuating mechanism comprises a needle having a spherically contoured tip that is seated on and unseated from the valve seat to open and close the flow through the fuel injector. When the fuel injector is open to flow, fuel passes through the lift opening that is created between the needle tip and the valve seat by the lifting of the tip from the seat. From there the fuel flow converges toward and enters the central circular hole. The orifices in the thin disc member are at the bottom of this central circular hole, but out of the direction of the converging flow that enters the hole, and as a result, the fuel flow must bend in order to pass to the orifices, and bend fairly sharply at that.
The purpose of each orifice in the thin disc orifice member is to inject a stream of fuel that is perpendicular to the plane of the orifice in accordance with a pressure vs. flow characteristic of the orifice. Such orifice members have heretofore been constructed as a flat disc that is disposed perpendicular to the main axis of the injector so that fuel is injected from each orifice as a stream that is parallel to that axis, or as a disc that has a centrally protruding conical dimple containing one or more orifices so that fuel is injected from each such orifice as a stream that is non-parallel to the injector axis, but is aimed in a desired direction. In actuality, injection streams from the orifices of thin disc orifice members are not perfectly ideal, but rather exhibit some degree of divergence.
To the extent, if at all, that the flow through an orifice of a thin disc orifice member may have been considered to be other than perfectly uniform at any location around the orifice during certain conditions of injector operation, the degree and nature of possible non-uniformity appear not to have heretofore been fully appreciated. The present invention is a result of the quite remarkable and unexpected discovery that for at least certain conditions of operation of certain fuel injectors, particularly at low injector lifts, there exists a rather startling disparity in fuel velocity vectors across an orifice. It is believed that this phenomenon is a consequence of the injector geometry that requires the flow to make the rather sharp bend described above as it passes from the lift opening to the orifice.
The nature of this phenomenon, which has been developed analytically and confirmed by empirical observation, involves the creation of a zone in which a portion of the liquid fuel flowing toward an orifice is recirculated before reaching the orifice. This recirculation may be considered as an eddy that, as it approaches the orifice, curves radially outwardly away from the orifice, then curves axially upwardly along the wall of the central circular hole, and then curves radially inwardly and finally again axially downwardly toward the orifice.
Briefly, the invention comprises the inclusion of an undercut in the central circular hole between the downstream terminus of the frustoconical seating surface and the thin disc orifice member. The undercut provides a space for the recirculation zone with the result that the recirculation zone is displaced farther radially outwardly thereby diminishing its adverse influence on the flows through the orifices of the thin disc orifice member.
The foregoing, along with further details and other advantages and benefits of the invention, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a presently preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention.